Recent portable terminal units such as pagers (radio call receiver) or portable telephone have been becoming more and more compact and also the functions have been expanded. For this reason, units each having a dedicated data terminal have been proposed to write data in the portable terminal units from outside as well as to take out data from the portable terminal units to outside. Also in the portable terminal units as described above is generally incorporated a chargeable battery (for instance, a Ni-Cd battery: a is chargeable nickel-cadmium battery in which nickel is used for anode and cadmium for cathode) and is also included a charging terminal.
However, in the conventional types of portable terminal units as described above, a dedicated data terminal is provided in addition to a charging terminal, which makes it difficult to minimize a size of portable terminal units and causes cost increase and also limits a freedom in designing portable terminal units.